Efficiently Sum Values Based on Conditions in Java Streams

Learn how to aggregate positive and negative values conditionally in Java streams using a single collect operation for cleaner and efficient code writing.
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Efficiently Sum Values Based on Conditions in Java Streams

In Java programming, handling collections of data is a common task, often requiring us to perform aggregations based on certain conditions. Imagine you have a list of sales represented by a class, and each sale includes a country and an amount which can be either positive or negative.

You might find yourself needing to calculate the sum of positive values and negative values separately, grouped by country. This is a standard problem in data processing. This guide will guide you through the solution using Java Streams, which allows us to write clean, efficient code.

The Problem

Let’s break down the requirement:

Given a list of objects of type Sale, defined as follows:

[[See Video to Reveal this Text or Code Snippet]]

Your data might look like this:

countryamountnl9nl-3be7.9be-7You want to compute a Map<String, Pair<BigDecimal, BigDecimal>> that gives you:

The sum of positive amounts by country.

The sum of negative amounts by country.

While it's straightforward to handle this with two separate streams, the challenge is to perform this task using a single stream operation.

The Solution

Steps to Achieve the Solution

Initialize the Stream: Start the stream from your list of sales.

Merge Function: Define how to merge two Pair objects when there are duplicate keys.

Example Code

Here’s how the implementation looks in Java:

[[See Video to Reveal this Text or Code Snippet]]

Testing the Function

Let’s test this function with a sample list of sales:

[[See Video to Reveal this Text or Code Snippet]]

Output

When you run the above test, you’ll see output similar to this:

[[See Video to Reveal this Text or Code Snippet]]

This output clearly shows the sums of positive and negative values for each country, done efficiently in a single stream.

Conclusion

Remember, mastering Java Streams not only helps you write cleaner code but also improves performance and maintainability of your applications.

Happy coding!